Variables and Expressions
Narrated by Horst
draw_tree(225, 35)
draw_tree(420, 45)
draw_house(720, 60)
draw_snow_person(300, 20)
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How to use variables (this chapter)
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How to write expressions (this chapter)
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How to create our own functions (the next two chapters)
How to Use Variables
Variable and Function Names
Good Variable Names
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temperature_in_celsius
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tree_position_1
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tree_position_2
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car_speed
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number_of_children
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simpson
Bad Names, that still work:
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temperatueInCelsius - Uses capital letters. Keep it lower case and use underscores.
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x - Too short, and not descriptive.
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Smith - Starts with a capital letter.
Names that don't work:
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tree position - Can’t use spaces
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4runner - Can’t start with a number
Constants
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Variables that don't change are constants
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They should be in all upper-case
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PI = 3.14159
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SCREEN_WIDTH = 800
How to Create Expressions
| Operator | Description |
|---|---|
| + | Addition |
| - | Subtraction |
| * | Multiplication |
| ** | Exponentiation |
| / | Division |
| // | Integer division (always rounds down) |
| % | Modulus (division remainder) |
Using Operators in Expressions
What's Different?
- Juxtaposition doesn't work - It doesn't multiply
- The '=' isn't an algebraic equality - It is an assignment
Juxtaposition Doesn't Work
Assignment Operators
| Operator | Description |
|---|---|
| = | Assignment |
| += | Increment |
| -= | Decrement |
| *= | Multiply |
| /= | Divide |
Increasing a Variable
Increment/Decrement Operators
Using Expressions In Function Calls
Order of Operations
average = 90 + 86 + 71 + 100 + 98 / 5
average = (90 + 86 + 71 + 100 + 98) / 5
